linux-kernel - Re: [PATCH v2 00/23] Update cache properties for arm64 DTS

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Date:   Mon, 7 Nov 2022 17:11:52 -0600
From:   Rob Herring <robh@...nel.org>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v2 00/23] Update cache properties for arm64 DTS

On Mon, Nov 07, 2022 at 04:56:53PM +0100, Pierre Gondois wrote:
> v2:
> - Update/Add patches for missed cache properties requiring to be
>   updated for the following platforns: bcm, amazon, arm, exynos,
>   freescale, marvell, mediatek, nvidia, socinext, tesla, ti.
>   Missed cache properties were detected using Rob Herring's branch:
>   https://github.com/robherring/dt-schema/tree/cache-rework
> - v1 of exynos, tesla were merged.
> - Updated wrong reference in commit message.
> - Added received Rb/Acked-by.
> 
> Align arm64 DTS to the DeviceTree specification v0.3 regarding
> cache properties. The patch-set mainly adds 'cache-level' or
> 'cache' compatibility properties.
> For one qcom DTS, level 1 cache nodes are removed as they should
> be in the cpu nodes.
> 
> On another node, it seems that the 'cache-unified' is under-used.
> cache-unified:
>   If present, specifies the cache has a unified or-
>   ganization. If not present, specifies that the
>   cache has a Harvard architecture with separate
>   caches for instructions and data.
> Only a few l2 cache nodes have this property, and in the absence
> of [|d|i]-cache-size properties (or other), the cache is assumed to be
> split.
> 
> The l2 cache of the Rockchip RK3308 platform is thus assumed to be
> split:
> l2: l2-cache {
> 	compatible = "cache";
> 	cache-level = <2>;
> };
> when the platform datasheet advertises a unified cache.
> 
> No modification/check was made to correct that due to the lack of
> cache information for most platforms.

I suppose in theory a split L2 is possible, but I think in practice that 
doesn't exist. The Arm ARM allows for such a thing, but this[1] says L2 
caches are unified. IMO, we should just define level 2+ is unified in 
the schema and we can relax that if ever needed. I've updated the cache 
schema branch[2] with that requirement.

Rob

[1] https://developer.arm.com/documentation/den0024/a/Caches/Cache-terminology
[2] https://github.com/robherring/dt-schema/tree/cache-rework